Example update for README.md

[charl]

The example listed in README.md seems to be dated.

    reply, err := s.ExecRPC(netconf.RPCGetConfig("running"))

Should most likely be:

    reply, err := s.Exec(netconf.MethodGetConfig("running"))

[nemith]

Good catch. Want to do a pull request?

[charl]

/me caught at being lazy

Sure, I'll also remove:

Today it only supports the SSH transport mechanism (and NETCONF 1.0 SSH framing)

As it looks like we do now have telnet support or is that just experimental?

[charl]

@nemith done in #10.